Numerous processes for controlling the dispersing of finely divided particles in solid propellant have been developed. In addition to controlling potlife of a propellant composition during the mixing and formulating procedure, the coating of finely divided particles such as an oxidizer, particularly, ammonium perchlorate, prevents or minimizes the reaction between the coated or encapsulated oxidizer with the other ingredients of the propellant or with the agents used to cure the system.
U.S. Pat. No. 3,480,488 issued to T. P. Rudy et al is an example of prior art process of "Self-Regulating Coating Process For Propellant Materials." This process is a process for the encapsulating of oxidizer particles which are incompatible with the other ingredients in the solid propellant composition. Due to the polar nature of the oxidizing agents, a polar monomer, tris(2-methylaziridinyl)phosphine oxide (MAPO), and a non-polar solvent n-hexadecane or purified alkane (boiling point 185.degree.-200.degree. C.) are required. Absolutely complete encapsulation is required in U.S. Pat. No. 3,480,488 because of the reactivity of the inorganic oxidizer with some of the other propellant ingredients.
More recently, U.S. Pat. No. 5,002,797, issued to applicant on Mar. 26, 1991, and assigned to the United States of America as represented by the Secretary of the Army, Washington, D.C., encompasses a process for aluminmum-encapsulated ammonium perchlorate by vapor deposition. This process yields a product which after being incorporated into a propellant composition achieves the following beneficial effects: (a) increasing the propellant's burning rate; (b) extending the storage life of interceptor motors; and (c) improving the propellant mechanical properties.
Solid propellant compositions employing ammonium perchlorate have also used ferrocene or the more expensive ferrocene derivative, liquid Catocene, the registered trademark for Syntex Chemicals, Inc. 2,2-bis(ethylferrocenyl)propane (C.sub.27 H.sub.32 Fe.sub.2), as a high burning rate accelerator.
The problem of migration of Catocene has been a concern. To inhibit the migration of Catocene from a propellant composition of rocket motor, into the liner-barrier, a larger amount is incorporated into the liner-barrier. For example, if 5% Catocene is incorporated into the propellant formulation, an amount of 25-30% Catocene in the liner-barrier is required to achieve the equilibrium conditions necessary to ensure no degradation of the propellant burning rate due to excessive migration out of the propellant.
The incorporation of Catocene has been contraindicated because of the tendency of the propellant to become increasingly sensitive to initiation by various stimuli with aging, but, because of the need of the burning rate augmentation that Catocene, and only Catocene, can provide, has necessitated its use in spite of the fact that there have been a number of serious accidents which have occurred with Catocene-containing propellants.
No satisfactory means have been discovered previously which would prevent the migration of Catocene when it is incorporated into a solid propellant. Thus, the need is highly recognized for a process to convert Catocene to a form which not only results in the reduction of its diffusibility and migratability in solid propellants but also reduces its sensitivity.
Therefore, an object of this invention is to provide a method of converting potential propellant ingredients which cannot be used because of their high reactivity, hygroscopicity, incompatibility, etc. into usable propellant ingredients.
A further object of this invention is to provide a method which employs coacervation to convert the high-burning rate accelerator, Catocene, into a coacervated product.